A synovial membrane of a synovial joint secretes synovial fluid into synovial cavity to absorb and reduce the impact and friction of joints caused by body movement. The synovial fluid can also serve as a medium for nutrients and metabolic waste transportation. Synovial fluid is a composition of a variety of structural biomolecules including polysaccharides, glycoproteins, and proteoglycans as well as functional enzymes such as protease and collagenase. In previous studies, it was found that albumin and hyaluronic acid may be critical molecules that associate with the tribological properties of artificial joints.
Young people often have joint injuries caused by loose ligaments, bacterial infections, gout or other factors. In elders' joints, wear of cartilage and constant collision between the bones result in degenerative osteoarthritis (OA or degenerative arthritis) and pain. When the pain affects motor ability, physical therapy or medications can be used in early stage. If a patient's symptom cannot be alleviated, eventually artificial joint arthroplasty needs to be performed to replace the worn joint so as to maintain motor ability.
The candidate materials commonly used in artificial joints and implants include polymers, metals and ceramics, among which ultra-high molecular-weight polyethylene (UHMWPE) and cobalt-chromium-molybdenum alloy (Co—Cr—Mo Alloy) are quite well known and widely used. However, an artificial joint is not a perfect substitute for an original joint, especially in view of that wear debris caused by friction is inevitable for an artificial joint. Wear debris particles can induce immune responses in the body, and more seriously, it can further lead to osteolysis. If not treated effectively, osteolysis will accelerate artificial joint loosening, which in turn reduces the life of artificial joints. Wear rate of an artificial joint primarily relates to the degree and frequency of a patient's motion, friction coefficient of the artificial joint material and how long the artificial joint has been used. Even though UHMWPE is a tough material with a lower wear rate, its debris is still a threat to a patient's health and life of the implant.
So far, there is still a need for a more effective lubricant to reduce friction and wear debris.